Implement Lab6 up to and including Exercise 4

Exercise 5 requries stdin so we will come abck to that once I figure out how
best to do that.

Primes generation could be more efficient.

week1.java

@@ -1,10 +1,12 @@
 import java.util.Calendar;
+import java.util.Scanner;
 import java.util.concurrent.ThreadLocalRandom;
 
 class runLabs {
     public static void main(String[] args) {
         new Lab4();
         new Lab5();
+        new Lab6();
     }
 }
 
@@ -13,11 +15,20 @@ class Section {
 
     public Section(int s) {
         this._sectionNumber = s;
+        this.printSection();
     }
 
     public int getSection() {
         return _sectionNumber;
     }
+
+    public void printSection() {
+        String title = String.format("Starting section %s", this._sectionNumber);
+
+        System.out.println("-".repeat(title.length()));
+        System.out.println(String.format("%s", title));
+        System.out.println("-".repeat(title.length()));
+    }
 }
 
 class Lab {
@@ -200,9 +211,132 @@ class Lab4 extends Lab {
     }
 }
 
+/**
+ * Keyboard input
+ */
 class Lab5 extends Lab {
     public Lab5() {
         super(5);
-        System.out.println(String.format("hi"));
+        new five1();
+    }
+
+    class five1 extends Section {
+        /**
+         * We will now look at how we can get user input from the keyboard. We will
+         * gloss over some
+         * of the details here, but give you just the information you need to start
+         * getting input and
+         * processing it.
+         */
+        public five1() {
+            super(1);
+            System.out.println(String.format("TBC"));
+            // Scanner keyboard = new Scanner(System.in);
+            // System.out.println("Please enter your name, followed by the return key?");
+            // String userEntry = keyboard.nextLine();
+            // System.out.println("Hello " + userEntry);
+            // System.out.println(String.format("%s", keyboard));
+        }
+    }
+}
+
+/**
+ * Loops
+ */
+class Lab6 extends Lab {
+    public Lab6() {
+        super(6);
+        new six1();
+        System.out.println(String.format("%n"));
+        new six3();
+        new six5();
+    }
+
+    /**
+     * Times tables
+     */
+    class six1 extends Section {
+        public six1() {
+            super(1);
+            int testNum = 6;
+            System.out.println(String.format("Times table for %d:", testNum));
+            writeTimesTable(7);
+        }
+    }
+
+    class six3 extends Section {
+        public six3() {
+            super(3);
+            int testNum = 13; // statistically the most prime of all numbers
+            System.out.println(String.format("Testing primes..."));
+            System.out.println(String.format("%d prime? %s", testNum, isPrime(testNum)));
+            System.out.println(String.format("%d prime? %s", 23, isPrime(23)));
+            System.out.println(String.format("%d prime? %s", 27, isPrime(27)));
+            System.out.println(String.format("%d prime? %s", 28, isPrime(28)));
+            System.out.println(String.format("%d prime? %s", 299, isPrime(299)));
+            System.out.println(String.format("Generating primes..."));
+            generatePrimes(1024);
+            System.out.println(String.format("Done!%n"));
+        }
+    }
+
+    class six5 extends Section {
+        public six5() {
+            super(5);
+            System.out.println(String.format("TODO / NOT IMPLEMENTED until we get stdin working"));
+        }
+    }
+
+    public void writeTimesTable(int num, int limit) {
+        for (int i = 0; i < (limit + 1); i++) {
+            System.out.printf("%d\t", num * i);
+        }
+    }
+
+    public void writeTimesTable(int num) {
+        int DEFAULT_LIMIT = 10;
+        writeTimesTable(num, DEFAULT_LIMIT);
+    }
+
+    public void generatePrimes(int upperLimit) {
+        // handle 2 as a special case
+        System.out.println(String.format("2"));
+        // for (int i = 3; i <= upperLimit; i += 2) {
+        for (int i = 2; i <= upperLimit; i++) {
+            // TODO: figure out smarter way of doing this, I'm sure primes must be at least 6 apart...
+            // Something about 2n ± 1 ?
+            // seive of Erasthotenes ..?
+            if (isPrime(i)) {
+                System.out.printf("%d\t", i);
+            }
+        }
+    }
+
+    /**
+     * But is it prime?
+     * @param  num Integer to test for primality
+     * @return if it's prime
+     */
+    public boolean isPrime(int num) {
+        boolean DEBUG = false;
+        if ((num == 2) || (num == 1)) {
+            return true;
+        }
+        if (num % 2 == 0){
+            return false;
+        } else {
+            int divisor = 3;
+            double numSquareRoot = Math.sqrt((double)num);
+            while (divisor <= numSquareRoot) {
+                if (num % divisor == 0) {
+                    return false;
+                }
+                divisor += 2;
+                if (DEBUG) {
+                    System.out.printf("%d\t", divisor);
+                }
+            }
+            return true;
+        }
     }
 }